Notice: On April 23, 2014, Statalist moved from an email list to a forum, based at statalist.org.
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
st: is this the correct statistical test to compare non-normally distributed count data
From
Gwinyai Masukume <[email protected]>
To
statalist <[email protected]>
Subject
st: is this the correct statistical test to compare non-normally distributed count data
Date
Tue, 21 Jan 2014 18:07:16 +0200
Hello Stata list,
I have the variable a_score which can take the values 0, 1, 2 up to 9.
I have two groups and I want to compare if a_score is the same
between the two groups. Since a_score is not normally distributed I
have used a non-parametric test and the p-value shows that a_score is
not significantly different between the two groups if p < 0.05 is
considered significant.
Have I used the correct test?
Kind regards,
Gwinyai
. swilk a_score
Shapiro-Wilk W test for normal data
Variable | Obs W V z Prob>z
-------------+--------------------------------------------------
a_score | 4610 0.99456 13.698 6.850 0.00000
.
. * non-parametric test
. ranksum a_score, by(group)
Two-sample Wilcoxon rank-sum (Mann-Whitney) test
group | obs rank sum expected
-------------+---------------------------------
Group 1 | 4504 10338974 10352444
Group 2 | 92 224932.5 211462
-------------+---------------------------------
combined | 4596 10563906 10563906
unadjusted variance 1.587e+08
adjustment for ties -2084329.2
----------
adjusted variance 1.567e+08
Ho: a_score(group==Group 1) = a_score(group==Group 2)
z = -1.076
Prob > |z| = 0.2818
*
* For searches and help try:
* http://www.stata.com/help.cgi?search
* http://www.stata.com/support/faqs/resources/statalist-faq/
* http://www.ats.ucla.edu/stat/stata/